As a one-off, accidents happen and sometimes have serious consequences.
As a pattern of injuries at the same nursery, I would be very unimpressed that they couldn't even tell me what had happened and "found her like that".
Yes, nursery staff turn their backs and are doing other stuff, but normally they have a sense of where the children are and what they are doing so most accidents are prevented (because they can see it heading that way, for example a child waving a heavy wooden toy about) or, at the very least, they have a good idea of how the accident happened even if they didn't actually see it (banged into the play kitchen, fell over a toy car etc.).